1. Field of the Invention
This invention relates to an ignition coil apparatus for use in a distributor for supplying a high voltage to the plug of an internal combustion engine at the time of igniting the internal combustion engine.
2. Description of the Prior Art
FIG. 12 shows an example of a prior art ignition coil for an internal combustion engine in which a permanent magnet is arranged in the closed magnetic path of a core. In FIG. 12, reference numeral 30 represents a case, 31 a container formed inside the case 30, 32 a primary coil stored in the container 31, 32a a bobbin to which the primary coil 32 is wound, 32b a hole formed at the center of the bobbin 32a, 33 a secondary coil stored in the container 31 and arranged around and concentrically with the primary coil 32, 33a a bobbin to which the secondary coil 33 is wound, and 34 a core for forming a single magnetic circuit for magnetically coupling the primary coil 32 and the secondary coil 33. This core 34 has two U-shaped cut cores 34a and 34b which are arranged in such a manner that their end surfaces face each other to form a ring-shaped core 34. The inner foot of the cut core 34a is inserted into the hole 32b of the bobbin 32a of the primary coil 32 from one side of the hole 32b whereas the inner foot of the cut core 34b is inserted into the hole 32b of the bobbin 32a from the other side. The end surfaces of these two inner feet are placed in contact with the permanent magnet 35 arranged therebetween. The outer foot of the cut core 34a and the outer foot of the cut core 34b are arranged along the outer wall of the case 30 to enclose outer portions of the primary coil 32 and the secondary coil 33 and the end surfaces of these two outer feet are in contact with each other. The above-mentioned permanent magnet 35 provides the core 34 with a magnetic flux 37 indicated by a dotted line which is opposite in direction to a magnetic flux 36 indicated by a one-dot chained line, generated in the core 34 while electricity is supplied to the primary coil 32. Numeral 38 denotes an insulating resin which is poured into the container 31 and solidified after the core 34 is attached to the primary coil 32 and the secondary coil 33 stored in the container 31.
Consequently, in the ignition coil apparatus shown in this FIG. 12, since the permanent magnet 35 provides the core 34 with the magnetic flux 37 opposite in direction to the magnetic flux 36 generated in the core 34 while electricity is supplied to the primary coil 32, the magnetic flux 36 generated in the core 34 by applying electricity to the primary coil 32 cancels the magnetic flux 37 generated by the permanent magnet 35 and is grown into a saturated magnetic flux which is large enough to saturate the core 34. Therefore, compared with the case where there is no permanent magnet 35, magnetic force stored in the core 34 increases and electric power output from the secondary coil 33 rises.
FIG. 13 is a side view of a distributor in which an ignition coil apparatus is arranged coaxially with a shaft rotating in synchronization with the rotation of an internal combustion engine and FIG. 14 is a sectional view of the ignition coil apparatus of the distributor.
In FIG. 13, reference numeral 20 represents a base, 21 the shaft which rotates in synchronization with the rotation of the internal combustion engine and is rotatably mounted on the base 20, 22 an ignition coil apparatus arranged coaxially with the shaft 21, 23 an electric unit comprising electronic circuits such as a crank angle sensor, power transistor and other electronic parts, 24 a cap, 25 a connector protruding outward from the electric unit 23, and 26 a screw. The base 20, ignition coil apparatus 22, electric unit 23 and cap 24 are assembled into a single unit in such a manner that the ignition coil apparatus 22 is mounted on the base 20 to which the shaft 21 is attached, the electric unit 23 is arranged on the ignition coil apparatus 22, and the cap 24 is placed over the electric unit 23.
In FIG. 14, numeral 1 represents a cylindrical case made of a synthetic resin having a bottom portion in the ignition coil apparatus 22 of FIGS. 13, 2 a hole formed at the center of the bottom portion of the case 1 for passing the shaft therethrough, 3 a container formed in the case 1 with the wall surrounding the hole 2 and the bottom portion and the outer wall of the case 1, 4 a primary coil arranged in the container 3 around the hole 2, 5 a secondary coil arranged in the container 3 around and coaxially with the primary coil 4, and 6 cores for forming four magnetic circuits for magnetically coupling the primary coil 4 and the secondary coil 5 by supplying a primary current to the primary coil 4. These cores 6 are stored in the container 3 and arranged around the hole 2 at intervals of a right angle so that they cross-chain the primary coil 4 and the secondary coil 5. Each core 6 is composed of a pair of U-shaped cut cores 6a and 6b arranged around the hole 2 at intervals of a right angle and astride the primary coil 4 and the secondary coil 5 from above and below in the direction of the center line of the hole 2, and the end surfaces of the cut cores 6a and 6b face each other in vertical direction so that the cores 6 are each ring-shaped to cross-chain the primary coil 4 and the secondary coil 5 at intervals of a right angle. The cut core 6a is integrated with the case 1 by insertion at the time when the case 1 is molded, whereas the cut core 6b is stored in the container 3 after the primary coil 4 and the secondary coil 5 are stored in the container 3. The inner foot of the cut core 6a is interposed between the primary coil 4 and the wall of the hole 2 whereas the inner foot of the cut core 6b is inserted between the primary coil 4 and the wall of the hole 2 from above, and the end surfaces of the inner feet of the two cut cores 6a and 6b are contacted to each other in a vertical direction. The other foot of the cut core 6a is interposed between the secondary coil 5 and the outer wall of the case 1 whereas the other foot of the cut core 6b is inserted between the secondary coil 5 and the outer wall of the case 1, and the end surfaces of the other feet of the two cut cores 6a and 6b are made apart from each other in vertical direction to form a gap 7 having a predetermined distance therebetween. Numeral 8 represents a synthetic resin cover for aligning the cut core 6b with the cut core 6a in vertical direction. The extending ends of the four arms of the covers 8 extend from the inner surface of the outer wall of the case 1 and fit in position determination portions of the case 1, and a back portion of the cut core 6b astride the opposing feet is arranged over the cover 8. Numeral 9 denotes an insulating resin which is poured into the container 3 and solidified after the cut core 6b is installed over the primary coil 4 and the secondary coil 5 stored in the container through the cover 8.
Therefore, in the ignition coil apparatus shown in FIG. 14, each time a primary current flows through the primary coil 4 upon ignition of the internal combustion engine, the secondary coil 5 which is magnetically coupled to the primary coil 4 by the core 6 generates a high voltage for igniting the internal combustion engine. At this time, since the core 6 is provided with a high magnetic field by the gap 7 while electricity is supplied to the primary coil 4, efficiency of magnetism stored in the core 6 by supplying electricity to the primary coil 4 is excellent. Moreover, since the ignition coil apparatus is structured such that the base, electric unit and gap are arranged around the shaft in tiers as shown in FIG. 13 and that a plurality of cores 6 are arranged around the hole 2 at intervals of a right angle to cross-chain the primary coil 4 and the secondary coil 5 as shown in FIG. 14, its volume efficiency is higher than the ignition coil apparatus shown in FIG. 12, which is extremely effective for reducing the size of the distributor.
Although the ignition coil apparatus shown in FIG. 12 is structured such that a single core is provided with a permanent magnet to increase output energy as described above, it is arranged decentrically with the shaft of the distributor. On the other hand, the ignition coil apparatus shown in FIG. 14 is arranged coaxially with the shaft of the distributor, is excellent in efficiency of magnetism due to the provision of the four cores 6, and has a structure that contributes to a reduction in the size of the distributor, but it has no permanent magnet.
Then, it is conceivable to obtain an ignition coil apparatus having a permanent magnet for a plurality of cores 6, excellent efficiency of magnetism and increased output energy. However, just the provision of a permanent magnet for each of a plurality of cores 6 increases the number of permanent magnets, the number of parts and the number of assembly steps, and accordingly, it is hard to adopt this approach immediately. In other words, when a permanent magnet is provided for each of the plurality of cores 6, even if this approach is limited to comparatively practical structures, the following structures are conceivable and it is impossible to implement this approach immediately.
(1) Permanent magnets are arranged on all the contact surfaces of the cut cores 6; PA0 (2) Permanent magnets are arranged on all the inner contact surfaces of the cut cores 6; PA0 (3) Permanent magnets are arranged on all the outer contact surfaces of the cut cores 6; PA0 (4) A permanent magnet is arranged in the existing gap 7 of each core 6; PA0 (5) Permanent magnets are arranged at positions other than the existing gap 7 of each core 6; PA0 (6) Permanent magnets are arranged in such a manner that they do not impair the usability of parts constituting each core 6; PA0 (7) Emphasis is placed on workability and parts constituting each core 6 have their own shapes; PA0 (8) Permanent magnets are arranged alternately on the inner and outer contact surfaces of the cores 6; PA0 (9) A permanent magnet is arranged in the entire gap; and PA0 (10) A permanent magnet is arranged in half of the gap and the other half of the gap is made an air gap 7.